An optical navigation device, such as an optical mouse, conventionally uses a packaged light-emitting diode (LED) to emit light onto a work surface. Typically, the light from the LED travels through a collimating lens and reflects off the work surface to a sensor. The reflection of the light produces a pattern that is captured by the sensor. The sensor can include, for example, a complementary metal-oxide semiconductor (CMOS) imager array. As an optical navigation device is moved relative to the work surface (or vice versa), successive images (frames) are rapidly captured and compared to measure the amount of movement. The difference between successive images indicates the amount of movement.
For a variety of reasons, an end user may desire a small form optical navigation device. In one instance, the end user may be a mobile professional that appreciates compact devices. In another instance, the end user may be a child and a smaller optical navigation device may be more suitable. In still another instance, the end user may simply desire a small form optical navigation device for its appearance.
Usually, one limiting factor on shrinking an optical navigation device is the size of the LED assembly. A typical LED assembly, such as a LED package, includes a reflector cone that redirects sidelight from the LED into a desired direction in addition to a bare LED die. However, utilizing a reflector cone only contributes to an increase in size. Furthermore, a LED package is approximately three times more expensive than a bare LED die.
Furthermore, sidelight and stray light from a light source may be difficult to fully capture and/or redirect, which can lead to a decline in the performance of the optical navigation device. Specifically, the stray light noise can interfere with the sensor's ability to detect movement of the optical navigation device. Further, since the light source emits light all directions and not just towards a work surface, if some of the light is not redirected, low illumination efficiency will result.